1. Field of the Invention
The present invention relates to a time difference adjustment circuit and, more particularly, to a time difference adjustment circuit that adjusts a difference in signal transmission delay time between a plurality of transmission channels. The present invention also relates to a method for adjusting the time difference.
2. Description of the Related Art
The transmission rate of a communication channel between computers has been dramatically improved. Under such a circumstance that a communication rate has thus been increased, a time difference between signals, which is caused by variations in design and production or a difference in ambient conditions such as an ambient temperature, is recognized as a significant problem during exchanging signals through a plurality of communication channels.
Conventionally, a strict design accuracy standard and strict manufacturing standard have been set for a high-speed communication channel between computers in order to reduce variations in signal transmission time, resulting in an increase of costs. As a method of automatically adjusting a difference in delay time generated in the communication between computers, there is known a method that uses a receiving-side computer for detecting and adjusting the time difference between signals transferred through a plurality of communication channels. However, in the conventional adjustment method, a complicated process is required which includes the steps of feeding-back a signal time difference detected by the receiving-side computer to a transmitting-side computer and adjusting the delay time in a delay circuit of the transmitting-side computer.
Patent Publication JP-11-225173A describes a technique that adjusts a delay time difference between signals without using a feedback signal in a signal transmission system exchanging the signals between computers. This technique includes the step of transmitting, via transmission lines, signals which have been delayed by variable delay circuits from a transmitting side, detecting reflected waves of the transmitting signals, calculating the delay time of the signals to be transmitted via the transmission lines based on the time difference between the signal transmission time and signal detection time on the transmitting side, and adjusting the delay time for the variable delay circuits.
In the technique described in JP-11-225173A, the signal delay time in each of a plurality of transmission lines is compared in the circuit provided for the each of the transmission lines, against a reference (expected) delay time. Therefore, it is necessary to set the reference delay time in a LSI for each transmission line or otherwise, to supply the reference delay time from outside. Further, variation in the reference delay time occurs in each circuit. Therefore, there is a question as to whether the above technique can measure an effective delay time in a high-speed transmission line.